The present invention relates to a pattern formation method, and more particularly, it relates to a lithography technique to form a resist pattern by using exposing light of a wavelength of a 1 nm through 180 nm band for forming a semiconductor device or a semiconductor integrated circuit on a semiconductor substrate.
In accordance with improvement in a semiconductor device or a semiconductor integrated circuit with higher integration and more refinement, there are increasing demands for further development of lithography techniques.
As exposing light used in forming a resist pattern through pattern exposure conducted on a resist film formed on a semiconductor substrate, KrF excimer laser or ArF excimer laser has already been put to practical use or is now being examined for practical use.
Also, a chemically amplified resist excellent in resolution and sensitivity is now considered to be used as a resist material.
In order to realize further refinement of a semiconductor device or a semiconductor integrated circuit, however, it is necessary to use, as the exposing light, a laser beam with a wavelength shorter than that of the ArF excimer laser, such as a Xe2 laser beam (with a wavelength of a 172 nm band), a F2 excimer laser (with a wavelength of a 157 nm band), a Kr2 laser beam (with a wavelength of a 146 nm band), an ArKr laser beam (with a wavelength of a 134 nm band), an Ar2 laser beam (with a wavelength of a 126 nm band) and a soft X-ray beam (with a wavelength of a 13, 11 or 5 nm band).
Therefore, the present inventors have formed a resist pattern from a resist film of a known chemically amplified resist through pattern exposure using a F2 laser beam. Now, a method of forming a resist pattern from a known resist material will be described with reference to FIGS. 3(a) through 3(d).
First, a resist material having the following composition is prepared:
Then, as is shown in FIG. 3(a), the resist material having the aforementioned composition is applied by spin coating on a semiconductor substrate 1 and heated, thereby forming a resist film 2 with a thickness of 0.3 xcexcm.
Next, as is shown in FIG. 3(b), the resist film 2 is irradiated with a F2 laser beam 4 through a mask 3 for the pattern exposure. In this manner, an acid is generated from the acid generator in an exposed portion 2a of the resist film 2 while no acid is generated in an unexposed portion 2b of the resist film 2.
Then, as is shown in FIG. 3(c), the semiconductor substrate 1 is heated with a hot plate, for example, at 100xc2x0 C. for 60 seconds.
Thereafter, the resist film 2 is developed with an alkaline developer, such as a 2.38 wt % tetramethylammonium hydroxide developer. Thus, the resist pattern is formed.
The resultant resist pattern 5 has, however, a defective pattern shape as is shown in FIG. 3(d).
The resist pattern 5 similarly has a defective pattern shape not only when the F2 laser beam is used as the exposing light but also when light of a wavelength of a 1 nm through 180 nm band is used.
In consideration of the aforementioned conventional problem, an object of the invention is forming a resist pattern in a good pattern shape through pattern exposure using light of a wavelength of a 1 nm through 180 nm band as exposing light.
The present inventors have concluded that the resist pattern has a defective pattern shape because the resist film has a high absorbing property against light of a wavelength of a 1 nm through 180 nm band, and examined various means for decreasing the absorbing property against light of a wavelength of a 1 nm through 180 nm band. As a result, it has been found that the absorbing property of the resist film against light of a wavelength of a 1 nm through 180 nm band can be decreased when both a cation and an anion of an onium salt used as an acid generator has a halogen atom.
Then, the inventors have examined the reason why the absorbing property against light of a wavelength of a 1 nm through 180 nm band can be decreased when both a cation and an anion of an onium salt used as an acid generator has a halogen atom. As a result, it has been found that a halogen atom has a property to shift the light absorption wavelength band inherent in the resist material.
Specifically, the pattern formation method of this invention comprises the steps of forming a resist film by applying, on a substrate, a chemically amplified resist including an acid generator of an onium salt having a halogen atom in both a cation and an anion thereof; and forming a resist pattern through pattern exposure by irradiating the resist film with exposing light of a wavelength of a 1 nm through 180 nm band and developing the resist film after the pattern exposure.
In the pattern formation method of this invention, since both the cation and the anion of the onium salt has a halogen atom, the peak of the light absorption wavelength of the resist film is shifted. Therefore, the absorbing property against light of a wavelength of a 1 nm through 180 nm band can be decreased. Accordingly, the transparency against the exposing light of a wavelength of a 1 nm through 180 nm band can be increased. As a result, through the pattern exposure by using the exposing light of a wavelength of a 1 nm through 180 nm band, a resist pattern can be formed in a good pattern shape.
In the pattern formation method, the halogen atom is preferably a fluorine atom.
In the pattern formation method, the cation of the onium salt preferably includes a phenyl group having a halogen atom.
In the pattern formation method, the anion of the onium salt is preferably a sulfonic acid ion having a halogen atom.
In the pattern formation method, the exposing light is preferably a F2 laser beam or an Ar2 laser beam.